Continuously variable transmission unit

ABSTRACT

A power input and output system for continuously variable transmission units of the type in which a nutatable traction body is supported both for rotation on the body axis and for nutational movement in which the body axis travels in a biconical path about a primary transmission axis. Power input and output members of the transmission unit are each linked to the nutatable body by gearing to be in direct torque transmitting relationship only with the nutatable body and so that the nutational component of movement is the result solely of traction surfaces on the body being in rolling frictional engagement against complementing and fixed traction surfaces.

BACKGROUND OF THE INVENTION

This invention relates to torque transmissions and more particularly, itconcerns improvements in continuously variable ratio transmission unitsby which the ratio range of such units is increased over the ratio rangeof presently available units without compromise in operating efficiencyand power density.

Various embodiments of continuously variable transmissions in which thepresent invention is particularly useful are disclosed in U.S. Pat. Nos.4,112,779 and 4,112,780, both issued Sept. 12, 1978 and in 4,152,946issued on May 8, 1979. In the type of transmission exemplified by thesepatents, three frame supported working bodies operate to transmit amechanical power input to a rotatable output at continuously variableoutput/input speed ratios within the design range of the transmission.For purposes of definition in this background discussion as well as inthe ensuing detailed description of the present invention and in theappended claims, the three working bodies may be termed respectively, an"alpha body" which is supported by the transmission frame to beconcentric with a first axis, a "beta body" which is concentric with asecond axis inclined with respect to and intersecting the first axis ata point of axes intersection, and an "omega body" carried by or formingpart of the frame to be concentric also with the first axis. Althoughany one of these three bodies may be rotatable on the respective axeswith which they are concentric, one of the three is held againstrotation to provide a reaction torque whereas the other two bodies arerotatable and coupled either directly or by gearing to the respectiveinput and output shafting of the transmission.

The capability for the continuously variable speed ratio in suchtransmissions is achieved by providing one of the beta and omega bodieswith a pair of rolling or traction surfaces which are surfaces ofrevolution about the concentric body axis and which are of variableradii along that axis in symmetry with the point of first and secondaxes intersection. Physically, such rolling surfaces will be provided byconical or cone-like members. The other of the beta and omega bodies isprovided with a pair of rolling or traction surfaces of revolution aboutthe concentric body axis but which are of relatively constant radius.The pairs of rolling surfaces on the beta and omega bodies are retainedin frictional engagement with each other at two contact points or zonescapable of positional adjustment to vary the ratio of the beta bodysurface radius (R_(b)) to the omega body surface radius (R_(w)). Thus,if the alpha body is rotatable at a velocity (α) about the first axis,the rotational speed of the beta body about the second axis in a fixedframe of reference is (β) and the rotational speed of the omega body onthe first axis is (ω), then the respective speeds of the three bodiesare related by the following equation:

    ω-α+(α-β) R.sub.b /R.sub.w =0.      (1)

A generally preferred mode of operating such transmissions has been toapply an input torque to the alpha body to carry the beta body innutation and hold the omega body against rotation (ω=0). The beta bodyis linked with an output shaft rotatable on the first axis by gearinghaving a ratio factor (k) which theoretically may be of any value andalso may be made either positive or negative depending on the particulargearing arrangement used. In light of the foregoing, where θ is unitoutput speed and taking into account the gearing ratio (k), theoutput/input speed ratio of the unit is determined by an equation:

    θ/α=1-kR.sub.w /R.sub.b.                       (2)

If, for convenience, the function R_(w) /R_(b) is designated as a radiusratio or (ρ), then Equation (2) becomes:

    θ/α=1-kρ.                                  (3)

The performance characteristics of such transmissions are described inan article entitled: "Performance of a Nutating Traction Drive" by P.Elu and Y. Kemper, paper no. 80-C2/DET-63, the American Society ofMechanical Engineers. In this Article, it is noted that extremely highoverall efficiencies are possible by appropriate selection of the gearratio factor (k) though with a corresponding reduction in thetransmission speed ratio range (e.g., 2.8/1.9 or 1.5 vs. 0.43/0 or ∞).The Article also makes reference to a "power multiplication factor"which results from the epicyclic motion of the nutating beta body ormember and which may be visualized as variation in the power "seen" atthe points of rolling friction engagement between the beta and omegabodies for a given power input. Also, the term "power density" is usedin the Article to express the power transmitting capacity of aparticular transmission unit for a given input speed.

Heretofore, all embodiments of transmissions of the type disclosed inthe aforementioned U.S. patents or "nutating traction drives" haveinvolved a direct connection of one of the unit input and unit output toa first of the alpha, beta or omega bodies, a retention of a second ofsuch bodies as a reaction member and preferably a gearing linkage (witha gear ratio k) of the other of the unit input and the unit output tothe third of such bodies. As a result, the attainment of high overallefficiencies and increased power densities was possible only with asevere curtailment of speed ratio range. In this respect, it should benoted that the radius ratio or (ρ) in Equation (3) is variable withinlimits dictated by the size and geometry of the transmission.

It is apparent, therefore, that continuously variable transmissions ofthe type mentioned are capable of achieving high operating efficiencies.It is equally apparent, however, that a need exists for expanding thespeed ratio range of such transmissions without compromise of operatingefficiency or of high power densities.

SUMMARY OF THE INVENTION

In accordance with the present invention, the nutatable beta body intransmission units of the general class described, is linked by separategear sets to respective input and output members of the transmissionunit. Preferably, the input and output members are supported directly bythe transmission unit frame for rotation about the primary or firsttransmission axis and each such member carries a keyed or otherwiserotatably fixed gear providing one of at least two gears in each of theseparate gear sets. The input or output member carried gear preferablymeshes directly with another gear of each gear set which is keyed orotherwise nonrotatably coupled directly for rotation with the beta bodyabout the second or nutating transmission axis. Although the beta bodyis carried rotatably by the alpha body as in past designs, in thisinstance, the alpha body rotates freely in the transmission frame and isnot connected either directly or by gearing to the input or the outputmembers of the transmission. Also, the unit is reversible in the sensethat it may be used as a speed reducer or inverter.

A primary object of the present invention is, therefore, to provide acontinuously variable transmission of the class described with anincreased range of speed ratios for a given high range of operatingefficiencies and power density. Other objects and further scope ofapplicability will become apparent from the detailed description tofollow taken in conjunction with the accompanying drawings in which likeparts are designated by like reference numerals.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal cross-section through a continuously variabletransmission unit incorporating the present invention;

FIG. 2 is a schematic cross-sectional view as seen on line 2--2 of FIG.1;

FIG. 3 is a schematic cross-sectional view as seen on line 3--3 of FIG.1;

FIGS. 4 and 5 are schematic cross-sectional views identical respectivelyto FIGS. 3 and 2 and included to facilitate an understanding ofrotational components when the direction of power transmitted throughthe unit of FIG. 1 is reversed;

FIG. 6 is a graph depicting the relationship of internal transmissiongear ratio factors and radius ratio factors to overall efficiency andunit speed ratios; and

FIG. 7 is a side elevation in partial longitudinal section andillustrating an alternative embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In FIG. 1 of the drawings, a continuously variable transmission unit orCVT is generally designated by the reference numeral 10 and shown toinclude a frame 12 of cylindrical configuration and closed at its endsby end plates or frames 14 and 16. Contained within the frame 12 are: analpha body 18 supported from the end frames 14 and 16 by bearings 20 and22, respectively, for rotation about a primary or first transmissionaxis 24; a beta body generally designated by the reference numeral 26and supported rotatably by the alpha body 18 through bearings 28 and 30for rotation about a second axis 32 inclined with respect to andintersecting the first axis 24 at a point S of axes intersection; and anomega body constituted in this instance by a pair of rings 34 and 36concentric with the first axis 24, fixed against rotation with respectto the frame 12 and shiftable axially along the first axis 24 toward andaway from the point S of axes intersection.

In the disclosed embodiment, the beta body 26 includes a pair ofoppositely convergent truncated cone members 38 and 40 supported by acentral shaft 42 journalled at opposite ends in the aforementionedbearings 28 and 30. The cone members 38 and 40 are carried by the shaft42 to permit relative rotary and axial movement of the cone members andthe shaft. The cone members are separated axially on the shaft by aball/ramp assembly 44. Although the assembly 44 is only partiallyillustrated in FIG. 1 to include a collar 46 splined for direct rotationwith the shaft 42 but permitting of axial movement relative to theshaft, and a pair of balls 48, it will suffice for purposes of acomplete understanding of the present invention to note that theassembly 44 operates as a torque coupling of the cone members 38 and 40with the shaft 42 and also to develop a thrusting force acting toseparate the cone members 38 and 40 along the axis 32 in response totorque transmission between the shaft 42 and the cone members 38 and 40.

The cone members 38 and 40 define exterior traction surfaces or betasurfaces 50 of revolution about the axis 32 and of a radius R_(b) whichis variable along the axis 32 as a result of the conical configurationof the surfaces 50 and 52. The beta surfaces forcibly engage a pair ofomega surfaces 54 and 56 formed on the interior of the rings 34 and 36at two points of contact P1 and P2 which are diametrically opposite fromeach other and located in a plane containing the first and second axes24 and 32. The omega surfaces 54 and 56 are of a constant or fixedradius R_(w) and are surfaces of revolution about the first axis 24.

The rings 34 and 36 are adjustable axially along the axis 24 as a resultof their connection in the disclosed embodiment to annular pistons 58and 60 contained respectively in annular chambers 62 and 64 in the frame12. By appropriate supply and exhausting of hydraulic fluid to thechambers 62 and 64, it will be appreciated that the rings 34 and 36 maybe moved axially toward and away from the point S and in a manner to besymmetrically positioned with respect to the point S at all times.

Supported for rotation in each of the end frames 14 and 16 independentlyof the alpha body 18 by bearings 66 and 68 are a pair of shafts 70 and72. In the interest of adapting terminology which is consistent withterms used in algebraic equations, the shafts 70 and 72 are referred toas "theta shafts" and may function to transmit a power input to or apower output from the unit 10 in a manner which will be described inmore detail below.

Each of the theta shafts 70 and 72 is linked by a separate gear set 74and 76, respectively, to the beta body 26 and specifically to the shaft42 thereof. In the disclosed embodiment, each of the gear sets 74 and 76includes two directly meshing gears. Thus, the gear set 74 includes abeveled pinion or sun gear 78 keyed or otherwise coupled for directrotation with the theta shaft 70 and a complementary bevel or planetgear 80 similarly coupled for direct rotation with the shaft 42 and thebeta body 26. The gear set 76, on the other hand, includes a ring gear82 coupled for direct rotation with the theta shaft 72 and which is indirect meshing engagement with a planet gear 84 coupled for rotationwith the shaft 42 and the beta body 26.

In the illustrated embodiment, the gears 78 and 80 of the gear set 74are of the same diameter and as such will have a ratio factor k1 equalto a numerical value of 1. Because the gears 78 and 80 would rotate inopposite directions, assuming the axis of both to be in a fixed frame ofreference, the ratio factor k1 will be algebraically negative. The ratiofactor k2 of the gear set 76 is equal to the diameter of the pinion gear84 divided by the diameter of the ring gear 82 and will be of anumerical value less than 1, for example 0.25. Because the gears 84 and72 will rotate in the same direction in a fixed frame of reference, theratio factor k2 will be algebraically positive.

In the operation of the unit 10, assuming a power input to the shaft 70and a rotational speed θ1 and an output from the shaft 72 at a speed θ2,the input/output speed ratio of the transmission is determined by theequation:

    θ1/θ2=(1-k1ρ)/(1-k2ρ).                 (4)

In FIGS. 2 and 3 the directions of rotation in the alpha body 18, thebeta body 26, as well as the theta shafts 70 and 72 are graphicallypresented. Thus, in FIG. 2, the power input at the speed θ1 in aclockwise direction tends to rotate the gear 80 and the beta body 26 ina counter clockwise direction. Because of the contacting beta and omegasurfaces, the alpha body will rotate in a clockwise direction. At theother end of the transmission, the ring gear 82 will be rotated at thespeed θ2 as a result primarily of the α component of rotation. Becausethe direction of the β is opposite to the α rotation, the θ speed may bevisualized as the velocity α of the alpha body diminished by the βrotation of the beta body 26.

In FIGS. 4 and 5, it is assumed that the shaft 72 is the power inputwhereas the shaft 70 is the output of the transmission. Thus if theshaft 72 and the ring gear is rotated in a clockwise direction (asviewed from the right end of FIG. 1) the gear 84 is prevented fromrotation in a clockwise direction because of its connection through thebeta body to the stationary omega rings 34 and 36. Accordingly, the ringgear 82 will operate to carry the beta body in nutation and developprimarily rotation in the alpha body 18. The direction of rotation inthe beta body will again be counter clockwise in a relative frame ofreference because the axis of the gear 84 is orbiting at the velocity α.At the output shaft 70, the rotational components α and β will combineor add to each other in driving the shaft 70 through the gear 78. In sodirecting a power input to the shaft 72 and taking a power output fromthe shaft 70 the unit 10 now functions as an inverter or a transmissionin which the output shaft is rotated at higher speeds than the inputshaft. Other operational characteristics such as the ratio range, therange of efficiency and power density remain unchanged.

If it is assumed further that the numerical value of the radius ratio ρ(see Equation (3) supra.) is variable between a maximum ρ↑=2.31 and aminimum ρ↓=1.14 and that the gear ratio factors k1 and k2 are,respectively, equal to -1 and +0.25, it will be seen that theinput/output speed ratios may be made to vary between approximately7.8:1 and 3:1. The ratio range of the transmission or the maximuminput/output speed ratio divided by the minimum input/output ratio isapproximately 2.6. As will be described below with reference to thegraph illustrated in FIG. 6, this range of speed ratios is more than11/2 times the ratio range attainable in prior designs in which theinput was connected directly to the alpha body 18. Moreover, because therange of input/output speed ratios avoids the condition in which theoutput shaft speed or θ approaches zero, power multiplication at thecontact points P1 and P2 is minimized with the result that operationthroughout the speed ratio range occurs at high efficiencies. The powerdensity of the unit 10 is, therefore, increased substantially.

In the graph of FIG. 6, overall efficiency of a nutating traction driveof the general class including the embodiment of FIG. 1 are plottedagainst speed ratio (output/input) to develop curves A, B, and C. Thegraph also includes a linear horizontal scale representing the variousgear ratio factors (k) and a hyberbolic scale coincident with a speedratio of unity or 1:1 and a gear ratio factor of zero to representvarious values of the radius ratio (ρ). Lines joining a specific gearratio factor (k) with minimum (ρ↓) and maximum (ρ↑) radius ratios in agiven transmission will intersect the abscissa axis at pointscorresponding to the upper and lower limits of speed ratio variation. Bytransposing these limits of speed ratio to the curves A, B, or C, theoverall efficiency of a machine for a given gear ratio (k) may bedetermined.

It is important to note that the curves in FIG. 6 are the result ofoperation with a constant power input connected directly to the alphabody or operation in accordance with Equation (3) supra. where thefunction α is constant. In the transmission of the present invention,however, the rotational speed α of the alpha body 18 is related to therespective theta shafts 70 and 72 by the equations:

    α=θ1/(1-k1ρ)                               (5)

or

    α=θ2/(1-k2ρ).                              (6)

Although the Equations (5) and (6) will yield the same value of α wherethe values of k1, k2 and ρ are given, both are provided to facilitaterelation of the values of α to a constant speed input which may beprovided either at the theta shaft 70 or the theta shaft 72.

From the foregoing and with reference to FIG. 6, it will be seen that bythe present invention, the respective gear ratio factors k1 and k2 areselected to be of opposite algebraic sign and of numerical values toprovide a range of speed ratios corresponding to high operatingefficiency ranges on each of the curves B and C. Although the two rangesof speed ratios are separated or non-contiguous in FIG. 6, due to thecurves being predicated on a constant α speed, the speed of the alphabody 18 or α in the present invention will vary so that the resultingrange of the speed ratios is, moreover, the product of multiplying theratio range provided using k1 at a constant α (i.e., 3.31/2.14 or 1.5)by the ratio range using k2 at a constant α (i.e., 0.72/0.42 or 1.7). Inother words, the range of speed ratios in accordance with the presentinvention given the indicated numerical parameters will be 1.5×1.7 or2.6.

In FIG. 7 of the drawings, an alternative embodiment of the invention isshown in which parts corresponding to the embodiment previouslydescribed with reference to FIG. 1 are designated by the same tens anddigits numerals but to which one hundred has been added. The primarydifference between the embodiment illustrated in FIG. 7 and that of FIG.1 is that the latter embodiment is particularly suited for transmissionapplications in which a power input and power output are located on thesame end of the transmission. Thus in FIG. 7, concentric theta shafts170 and 172 are journalled in the end frame 116. The theta shaft 170 iskeyed directly to a sun gear 178 which is in mesh with a planet gear 184keyed for rotation with the beta body in the same manner as either ofthe gears 80 and 84 of the previous embodiment. The planet gear 184 alsomeshes with an internal ring gear 182 fixed for rotation with theoutside theta shaft 172. A pinion gear 190 is keyed to the shaft 172.

The operation of the embodiment in FIG. 7 is the same as that of FIG. 1and needs no further discussion except to note that where the thetashaft 170 is the input shaft to the transmission 110, the unit willoperate as a reducing transmission with the gear ratio factor k1 beingthe diametric ratio of the gears 178 and 184 and the factor k2 being thediametric ratio of the gear 184 to the ring gear 182. Power output willbe taken from the shaft 172 and pinion gear 190.

The embodiment of FIG. 7 is particularly suited for use in transmissionapplications where the linear space available in a drive line for thetransmission is limited. An example of such an application is afront-wheel drive automotive vehicle in which an engine or power plant,the transmission and drive wheels are located one above the other.

Thus it will be seen that as a result of the present invention, a highlyeffective continuously variable transmission unit is provided by whichthe speed ratio range is increased in a very simple manner and withoutcomplex structure. It will also be apparent to those skilled in the artfrom the preceding description that modifications and/or variations maybe made in the embodiments disclosed herein without departure from thepresent invention. Accordingly, it is expressly intended that theforegoing description is illustrative only, not limiting, and that thetrue spirit and scope of the present invention be determined byreference to the appended claims.

I claim:
 1. In a continuously variable transmission having a rotatableinput, a rotatable output, a frame, an alpha body supported by saidframe for rotation about a first axis, a biconical beta body supportedby said alpha body for rotation on a second axis inclined with respectto and intersecting said first axis at a point of axes intersectionlocated centrally along the length of said beta body so that movement ofsaid second axis is confined to nutation on said point and about saidfirst axis, said beta body having a pair of beta traction surfaces ofrevolution about said second axis one such surface being located on eachside of said point of axes intersection, means for defining a pair ofomega surfaces of revolution about said first axis, said beta and omegasurfaces being in rolling friction engagement with each other at twopoints in a plane containing said first and second axes, said beta andomega surfaces further defining a radius ratio which is variable uponshifting the location of said points of rolling friction engagementrelative to said point of axes intersection, the improvementcomprising:first means for supporting said alpha body for rotation aboutsaid first axis dependent solely on the speed at which said second axisis driven in nutation about said first axis by said beta body; secondmeans for drivingly coupling said input and said beta body and defininga first gear ratio factor; third means for drivingly coupling said betabody and said output and defining a second gear ratio factor differingfrom said first gear ratio factor; and said first and second gear ratiofactors being related to said variable radius ratio so that the range ofoutput/input speed ratios of the transmission is greater than the rangeof such speed ratios attainable by said radius ratio alone.
 2. Thetransmission of claim 1 wherein said first and second gear ratio factorsare of opposite algebraic signs.
 3. The transmission of claim 2 whereinsaid first and second gear ratio factors are of different numericalvalues.
 4. The transmission of claim 1 wherein said second meansincludes a sun gear rotatable on said first axis and planet gear meansrotatable on said second axis with said beta body and in meshingengagement with said sun gear, and said third means includes a ring gearrotatable on said first axis and in mesh with said planet gear means. 5.The transmission of claim 4 wherein said sun and ring gears are atopposite ends of said beta body, and said planet gear means includesseparate pinion gears fixed at opposite ends of said beta body.
 6. Thetransmission of claim 4 wherein said planet gear means includes a singlepinion gear fixed to one end of said beta body, said sun and ring gearsbeing mounted for independent rotation at one end of said beta body andboth being in meshing engagement with said single pinion gear.
 7. Thetransmission of claim 1 wherein said radius ratio (ρ), said first gearratio factor (k1) and said second gear ratio factor (k2) are related tothe speed ratio (θ1/θ2) by the equation:

    θ1/θ2=(1-k1ρ) (1-k2ρ),

said first gear ratio factor (k1) being less than zero or negative andsaid second gear ratio factor (k2) being more than zero or positive. 8.The transmission of claim 7 wherein the function k2ρ is always lessthan
 1. 9. The transmission of claim 1 wherein said second meansincludes a gear set having a sun gear intermeshed with a planet gear.10. The transmission of claim 1 wherein said third means includes a gearset having a planet gear intermeshed with a ring gear.